1. Field of the Invention
The present invention relates to a method of forming a thin film pattern on a substrate and a method of forming a magnetoresistive element including the thin film pattern.
2. Description of the Related Art
Hitherto, in a thin film magnetic head and an electronic/magnetic device such as a semiconductor device, various kinds of thin film patterns are often used. For example, in a thin film magnetic head, a magnetoresistive (MR) element in which magnetic thin films and the like are stacked is used. In a semiconductor device, a wiring pattern constructed by conductive thin films is used. As such thin film patterns, not only a thin film pattern of an island-shape or a band shape, in some cases, a thin film pattern having a through hole is used.
One of methods of forming a thin film pattern is dry etching using a resist pattern as a mask. In the method, first, a thin film is formed on a whole substrate and, after that, a resist pattern having a desired pattern shape is formed by photolithography on the thin film. Subsequently, undercut is formed in the resist pattern. Further, by performing dry etching such as ion milling using the resist pattern in which the undercut is formed as a mask, a thin film pattern having a desired shape is formed. The dry etching is disclosed in, for example, translated national publication of patent application No. 2003-517693.
In recent years, miniaturization of electronic/magnetic devices is proceeding remarkably and, in association with it, a finer thin film pattern is in increasing demand. However, in the case of forming a fine thin film pattern by using the dry etching, it is difficult to obtain a thin film pattern of high precision. Specifically, at the time of forming a fine thin film pattern, the dimension of the resist pattern has to be also reduced. When the dimension of the resist pattern becomes extremely small, the shape of the resist pattern is deformed due to heat or the like applied at the time of dry etching, and an error tends to occur in the dimensions of a thin film pattern to be formed due to displacement from the dimensions of the initial resist pattern formed. In addition, as shown in FIG. 42, an end portion 117T of a resist pattern 105 heated is often rounded. Consequently, at the time of dry etching, a large amount of a re-attachment 109 is attached around the resist pattern 105. The inclination of an end face 117S becomes gentle, and the contour of a thin film pattern 117 becomes unclear. In such circumstances, a thin film pattern forming method capable of realizing high-precision dimensions without causing a trouble in lift-off operation even in the case of using a resist pattern of fine dimensions is requested. In the case of forming a fine thin film pattern by using the dry etching as described above, a problem such that a high-precision thin film pattern cannot be obtained due to occurrence of a burr may occur. To be specific, to form a fine thin film pattern, the dimension of the resist pattern has to be also reduced, so that the width and height of the undercut portion in the resist pattern have to be also reduced. However, when the dimensions of the undercut portion become extremely small, as shown in FIG. 42, part of the thin film removed from above a substrate 101 at the time of dry etching is re-attached as a re-attachment 109 around an end face of an undercut portion 108 of the resist pattern 105. Further, a case occurs such that the resist pattern 105 and the end face or the top face of the thin film pattern 117 to be formed are connected. In such a case, an operation of lifting off the resist pattern 105 becomes impossible. Even if the lift-off operation can be performed, a burr occurs in the peripheral portion of the thin film pattern 117. Therefore, a thin film pattern forming method capable of performing a smooth lift-off operation without causing a burr even in the case of using a resist pattern having small dimensions is desired.